This invention relates to a semiconductor light emitting device and a semiconductor light emitting apparatus, and more particularly to a semiconductor light emitting device and a semiconductor light emitting apparatus having improved extraction efficiency for light emitted from the active layer.
Semiconductor light emitting devices such as LEDs (light emitting diodes) and LDs (laser diodes) provide various emission wavelengths, high emission efficiency, and long lifetime while being compact in size. For this reason, they are widely used for display, lighting, communication, sensor, and other devices.
In such a semiconductor light emitting device, a semiconductor multilayer film including an n-type cladding layer, active layer, p-type cladding layer, and the like is formed on a substrate of GaAs or sapphire by direct epitaxial growth, or by lamination with a heterogeneous substrate. Electrodes are further formed on the n-type and p-type layers, respectively (e.g., Japanese Laid-Open Patent Applications 2002-353502 and 2001-217467).
However, this type of semiconductor light emitting device does not have sufficiently high extraction efficiency for light emitted from the active layer.
More specifically, the light emitted downward from the active layer is incident on the electrode provided under the substrate. However, the substrate has an alloyed region formed with the electrode material near the interface with the electrode. This causes a problem that the light emitted from the active layer is prone to absorption, which leads to a certain loss inside the chip.
In addition, the light reflected from the lower electrode is attenuated by optical absorption in passing through the active layer. This causes a problem that the reflected light cannot be fully exploited.
There is another problem that total reflection is likely to occur at the side face and the like of the chip. More specifically, the above-described LED is typically processed into a rectangular parallelepiped shape having six smooth faces by cleavage and dicing, and covered with mold resin or the like. However, due to the large difference between a high refractive index of the semiconductor crystal (about 3.5) and a low refractive index of the mold resin (about 1.5), total reflection is likely to occur at the interface therebetween. This decreases the probability that the light emitted inside the chip is extracted outside the chip.
An approach to improving the decrease of light extraction efficiency is to roughen the surface by wet etching or the like to form asperities (e.g., Japanese Laid-Open Patent Application 2001-217467). However, surface roughening is not effective for extracting light emitted toward the bottom face inside the chip mounted on a packaging member.